1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to a linear power amplifier (LPA) shelf in which a plurality of LPA types are supported with one LPA shelf according to each LPA installation and the number of frequency assignments (FAs) supported.
2. Background of the Related Art
Generally, a base station for a mobile communication system includes a LPA installed in a shelf. The LPA is used to amplify signals which are transmitted to subscribers on the basis of respective communication sectors.
FIG. 1 is a view schematically illustrating a configuration of a related art base station for a mobile communication system. Referring to FIG. 1, the base station includes a wireless device 100, a digital processing device 110, a BTS interconnection network (BIN) 120 and a processor 130.
The wireless device 100 processes a wireless signal for a wireless terminal. In other words, the wireless device 100 includes a band-pass filter (BPF) 102, a high power amplifier (HPA) 104, an LPA 106 and an RF transceiver 108. The wireless device 100 performs a common air interface (CAI) process, a wireless signal transmission/reception function, an RF signal up/down conversion function, an RF signal power amplification function and a wireless noise rejection function. The digital processing device 110 performs a channel coding/decoding related function, an interface function according to the sectors, and an analog common function for modulation/demodulation.
The BIN 120 routes packet data in the base station. In other words, the BIN 120 performs functions of routing and transmitting/receiving traffic information between the digital processing device 110 and a control station, as well as routing and transmitting/receiving control information between the processor 130 and the control station. The processor 130 controls the base station and functions to receive and divide TOD information of a global positioning system (GPS). According to the number of frequency assignments (FAs) and failure of LPA, 1:1 type, redundancy type and 2 way combiner type are respectively applied to an LPA shelf of the base station configured as discussed above.
FIG. 2 is a view schematically illustrating a configuration of a related art LPA shelf of a redundancy LPA type. Referring to FIG. 2, the LPA shelf to which the redundancy LPA type is applied comprises an LPA unit 200 and a switch unit 210. The switch unit 210 includes two switches 214 and 218 positioned at the front and back of the LPA unit 200.
The LPA unit 200 includes three LPAs (i.e., LPA1 200a, LPA2 200b and LPA3 200c) and a redundancy LPA (i.e., LPA4 200d). The redundancy LPA can be substituted for one abnormally performing LPA of the three LPAs 200a, 200b and 200c. When an LPA is performing abnormally, it is said to be in an abnormal state. Here, the LPA1, the LPA2 and the LPA3 cover an alpha sector, a beta sector and a gamma sector, respectively. In other words, signals to be transmitted to the alpha sector, the beta sector and the gamma sector are amplified by the LPA1 200a, the LPA2 200b, and the LPA3 2001c, respectively. If one of among the three LPAs 200a, 200b and 200c is in an abnormal state, the redundancy LPA, (i.e., LPA4 200d) is substituted for the abnormal LPA in order to maintain coverage.
For example, in case the LPA1 200a is in an abnormal state and cannot amplify signals to be transmitted to the alpha sector, the 3:4 switch 214 and the 4:3 switch 218 are switched from the LPA1 200a to the redundancy LPA4 200d. Accordingly, the signal to be transmitted to the alpha sector is inputted to the LPA4 200d and amplified to a predetermined level.
As described above and shown in FIG. 2, the switch unit 210 comprises the 3:4 switch 214 and the 4:3 switch 218. The 3:4 switch 214 is positioned at the front and back of the LPA unit 200 and inputs the signals for each sector to corresponding LPAs, and the 4:3 switch 218 switches the amplified signals outputted from the LPA unit 200 to transmit them to corresponding sectors. At this time, the switch unit 210 switches the signals to the LPA4 200d if the LPA for amplifying the signals for each sector is in the abnormal state.
Generally, one LPA accommodates 2 FAs. If the subscriber capacity of the corresponding base station increases or the number of FAs increases to 3 or 4 due to the change of the external environment, the LPA shelf changes to a 2 way combiner type as shown in FIG. 3. In this case, the LPA shelf provided with the related art redundancy type should be removed from the base station and replaced with a LPA shelf of a 2 way combiner type.
FIG. 3 is a view schematically illustrating a configuration of the LPA shelf of a related art 2 way combiner type. Referring to FIG. 3, the LPA shelf of 2 way combiner type comprises a signal dividing unit 300, an LPA unit 310 and a signal combining unit 320.
The signal dividing unit 300 provides the signals for each sector to the corresponding LPAs, via paths divided into a first path and a second path. The signal dividing unit 300 includes a first signal divider 300a, a second signal divider 300b and a third signal divider 300c. Signals that are to be transmitted to an alpha sector, a beta sector and a gamma sector are inputted to the first signal divider 300a, the second signal divider 300b and the third signal divider 300c, respectively. Each of the signal dividers 300a, 300b and 300c comprises an internal switch for separately providing the signals via at least two divided paths.
In the LPA unit 310, each of the alpha, beta and gamma sectors are provided with two LPAs. In other words, the LPA unit 310 comprises an LPA1 312a and an LPA2 312b for amplifying the signal to be transmitted to the alpha sector, an LPA3 314a and an LPA4 314b for amplifying the signal to be transmitted to the beta sector and an LPA5 316a and an LPA6 316b for amplifying the signal to be transmitted to the gamma sector. From the above description and considering that the LPA shelf of 2 way combiner type used in case the subscriber capacity increases and the number of FAs is 3 or 4, those skilled in the art will understand that two LPAs covering each sector are provided with respect to each sector.
The signal combining unit 320 combines the amplified signals according to the sectors. The signal combining unit 320 receives the amplified signals via two paths for each sector and combines two amplified signals provided by the corresponding two LPAs into one signal. The signal combining unit 320 includes a first signal combiner 320a, a second signal combiner 320b, and a third signal combiner 320c, which are used to combine each sector signal.
For example, in an exemplary embodiment where an output signal of the alpha sector is 60 watts and the number of allocated FAs is two, the LPA shelf of the redundancy type accommodates 30 watts per one FA. In the LPA shelf of the 2 way combiner type shown in FIG. 3, at least 3 FAs should be allocated. If the number of allocated FAs is 4, the LPA shelf of the 2 way combiner type accommodates 15 watt per one FA. When the first signal divider 300a receives the signals to be transmitted to the alpha sector, gains of the signals each of which has 15 watts (W) are amplified via two paths by the LPA1 312a and LPA2 312b and then combined using a phase combination method by the first signal combiner 320a, thereby outputting signals with a total of 30 W.
If either the LPA1 312a or the LPA2 312b changes to an abnormal state in the LPA shelf of the 2 way combiner type, the signal dividing unit 300 and the signal combining unit 320 can disconnect the corresponding paths, so that the loss due to signal division and signal combination is prevented. While an entire gain is maintained constantly, the output per FA decreases to half the gain. Accordingly, although service areas according to the FAs of sectors are reduced, the service is not stopped, so that the redundancy LPA, shown in FIG. 2, for preventing the service from being stopped is not required.
However, since the related LPA shelf itself is configured to be adaptable to respective LPA types, the LPA shelf must be removed from the base station and another LPA shelf must be substituted for the LPA shelf whenever an external situation occurs.
In addition, in the prior art, since the base station should be turned off so as to substitute the LPA shelf, the service is stopped for a long time until the LPA shelf is replaced completely. There is also a loss of manpower due to the physical replacement of the LPA shelf.